The majority of vehicles produced today include a cruise control system, or speed control system, which automatically controls the speed of a motor vehicle when operating in a cruise control mode. The cruise control speed is set by an operator of the vehicle to establish a vehicle speed preferred by the operator. The cruise control has been found particularly useful on long trips for improving the driver's experience by reducing driver fatigue resulting from extended physical or mental exertion. In addition, operating the vehicle in cruise control often reduces vehicle operating costs, since an engine operating under control of the cruise control system can achieve better fuel mileage.
Gear selection in an automatic transmission when paired with an engine operating in a cruise control mode, however, can be challenging. In many cruise control systems, the control system often selects a gear that places the engine at a relatively low speed for fuel efficiency purposes. However, known cruise control algorithms reacting to variations in road conditions can result in the vehicle speed exhibiting oscillatory behaviour about the cruise set speed. These oscillations can trigger gear shifts, especially when the cruise control system is operating the vehicle at a low engine speed. When operating at a low engine speed, the transmission downshifts to a lower gear to avoid operating the engine below a minimum speed. Consequently, even though the cruise control system can maintain the vehicle speed at a value close to the desired speed, the vehicle experiences a high frequency of gear shifts. The increased frequency can be unacceptable resulting in excessive transmission wear and driver aggravation.